Panchromatic imagery has lower spectral resolution and higher spatial resolution than multispectral imagery. Conversely, multispectral remotely-sensed imagery has higher spectral resolution and lower spatial resolution. While many methods have attempted to marry the two to achieve the best of both, they often result in the worst of both instead. For example, in part because the multispectral bands, specifically the red-blue-green bands, are not spectrally co-extensive with the full panchromatic band, colors are often distorted when attempting to pan sharpen the multispectral image with the panchromatic image.
One well-known color transform method in image processing is called Hue Intensity Saturation, or HIS, transform. The HIS transform is described in, for example, Gonzalez and Woods, Digital Image Processing, Section 6.2.3, pages 407-412, Pearson Education Inc, Upper Saddle River, N.J. 07458, which is incorporated here for all that it discloses. The HIS transform converts the red, green and blue (RGB) components of pixels in the multispectral image into values for hue (H), intensity (I) and saturation (S). When manipulating an image in the HIS color space, the values are independent so manipulation of one will not affect the others. Thus, intensity I may be manipulated without affecting the hue H or saturation S. When the manipulations are complete, the HIS color space is changed back to an adjusted RGB in a process known as reverse transformation. The multispectral image is thus “sharpened.”